Quick answer

Privacy Badger (EFF) is the purest learning-based tracker blocker; Ghostery gives the richest tracker-detail UI; DuckDuckGo Privacy Essentials bundles search + tracker blocking; PrivacyGuard is the newest, with per-site privacy scoring. All four are free. Pick by how much UI control you want.

At a glance

Extension	Method	Open source	Blocks ads	Privacy score
Privacy Badger	Heuristic learning	Yes (EFF)	No (by design)	No
Ghostery	Curated tracker DB	Partial	Yes (opt-in)	Limited
DuckDuckGo	Curated + Smarter Encryption	Yes	No	Yes (Grade A-F)
PrivacyGuard	Curated lists + behavioural	Yes	Optional	Yes (0-100 + breakdown)

Privacy Badger

EFF-built, heuristic. Does not use tracker lists — it learns, over time, which domains look like trackers based on behaviour. Strengths: unbiased, no block-list politics. Weakness: takes time to "warm up" on a new install; not as aggressive as curated-list blockers.

Ghostery

Longest-running tracker detection. Ghostery's UI shows every tracker on a page with category labels. Good for users who want to see exactly what is happening. The consumer product is free; Ghostery also operates a paid intelligence business selling anonymised tracker data to advertisers and researchers — some users find this uncomfortable (disclosed in their privacy policy).

DuckDuckGo Privacy Essentials

Bundles tracker blocking, HTTPS upgrading, and a Privacy Grade (A-F) per site. Integrates with the DuckDuckGo search engine. Good default choice for non-technical users.

PrivacyGuard

Chrome/Edge/Firefox, Manifest V3. Combines curated block lists with a per-site 0-100 Privacy Score factoring TLS quality, tracker count, fingerprinting attempts, and cookie practices. Integrates with the Gera ecosystem (GeraCompliance, Breach Check).

Who should pick which

Privacy purist: Privacy Badger.
Non-technical family member: DuckDuckGo Privacy Essentials.
Power user who wants detailed per-tracker UI: Ghostery or PrivacyGuard.
Open-source preference with per-site scoring: PrivacyGuard.